All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Working in TV channel transmission and the like depends on what is transmitted on it such as serials and other material. So, if what is transmitted is Halaal, then working in it is Halaal. And if what is transmitted is Haraam such as the indecent serials, lewd songs and the like, then working in it is Haraam.
You have stated that the content of that channel is mainly Urdu serials and you have to know that rulings are based on what is most likely to be the case. It is known that such serials have many evils that Islam has prohibited. Thus, hasten to leave working in that channel.
Finally, if you were ignorant about the prohibition of working in it, repented from it and gave up doing it, then you are excused from what had happened in the past and there is nothing wrong with benefiting from what you have earned from it.
Allaah Knows best.